Well, before one can really talk about legalization (decriminalization is okay; U.S. jails are full enough already), you need to focus on providing reasonably objective data to legislators (and the population in general) so they can make coherent decisions on something beyond crime rates as correlated with substance use, be they personal decisions or laws regarding individual substances or substance categories. What those laws end up being may differ from country to country, as per local social expectations, perceived level of social stability, maturity of thought etc. So it's kinda difficult to draft out one Big Solution and lump everyone with it.
Thing is, such a task may be Sisyphean in nature due to, again, raising interest more than raising awareness, especially given that peer pressure can be a large factor in experimenting with various substances rather than an informed decision of "Okay, I think this won't turn out too badly, and if others tell me it's becoming a problem I'll admit it's a problem and seek professional help." (train of thought that ought to apply to a lot of things beyond substance use). There's also the matter of different individuals' predispositions. While some will happily remain at pot or will pop some LSD now and then, there will also be some that end up existing solely for the next high.
Let adults do what they want with their own bodies.
Well, it's not solely their own bodies that are affected. Friends and family, emotionally strained, strangers and their possessions endangered. It's not a decision that revolves solely around one's self, which is one of the more easily-identifiable things that make the problem difficult to give a clear-cut answer to. Then again, it's not exclusively adults that become addicted.
Also, the idea of a "government subsidied company focused on profit" selling drugs is naive at best, stupid at worst, because the competition can undercut you, because they do stuff and cut corners that a "government subsidied company focused on profit", can't (or oughtn't) do. Like cutting drugs with rat poison.
I guess first, before talking about legalization, one must ask "Are the individuals comprising today's society arguably mature enough to make informed decisions about something that can so gravely affect them and those around them?". Personally, I don't think so. While some individuals may, indeed, be capable of making the decision in an informed manner and of understanding the consequences, for the greater masses, "Derp, Respect mah authoratah" as someone so adorably brainfarted at me recently, may be a more valid option.
To paraphrase Robert Heinlein and make a not-altogether-kosher analogy of my own, when the steak ends having a chance to make the diners choke to the point you need an on-site EMT
team, and the chokees thrash around smacking those nearby, then maybe, just maybe, banning steak (or at least selling it) may be reasonable.
Edit: Goddamn pleonasms.